drm/i915: Fix oops in vlv_force_pll_on()

intel_pipe_will_have_type() doesn't just look at the passied in
pipe_config, instead it expects there to be a full atomic state behind
it. Obviously that won't go so well when vlv_force_pll_on() just uses a
temp pipe_config. Fix things by using pipe_config->has_dsi_encoder
instead intel_pipe_will_have_type(INTEL_OUTPUT_DSI) to check if we need
to actually enable the DPLL.

Here's an example oops for reference:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
IP: [<ffffffffa0389a5b>] intel_pipe_will_have_type+0x15/0x7b [i915]
PGD 7acda067 PUD 72696067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
Modules linked in: i915 i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm intel_gtt agpgart netconsole psmouse atkbd iTCO_wdt libps2 coretemp hwmon efi_pstore intel_rapl punit_atom_debug efivars pcspkr i2c_i801 r8169 lpc_ich mii processor_thermal_device snd_soc_rt5670 intel_soc_dts_iosf snd_soc_rl6231 i2c_hid hid snd_intel_sst_acpi snd_intel_sst_core snd_soc_sst_mfld_platform snd_soc_sst_match snd_soc_core i8042 serio snd_compress snd_pcm snd_timer snd i2c_designware_platform sdhci_acpi i2c_designware_core soundcore sdhci pwm_lpss_platform mmc_core pwm_lpss spi_pxa2xx_platform evdev int3403_thermal int3400_thermal int340x_thermal_zone acpi_thermal_rel sch_fq_codel ip_tables x_tables ipv6 autofs4
CPU: 3 PID: 290 Comm: Xorg Tainted: G     U          4.6.0-rc4-bsw+ #2876
Hardware name: Intel Corporation CHERRYVIEW C0 PLATFORM/Braswell CRB, BIOS BRAS.X64.X088.R00.1510270350 10/27/2015
task: ffff88007a8dd200 ti: ffff880173ac4000 task.ti: ffff880173ac4000
RIP: 0010:[<ffffffffa0389a5b>]  [<ffffffffa0389a5b>] intel_pipe_will_have_type+0x15/0x7b [i915]
RSP: 0018:ffff880173ac7928  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff880176594000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000009 RDI: ffff880176594000
RBP: ffff880173ac7930 R08: 0000000000019290 R09: 0000000000000000
R10: ffff880173ac7890 R11: 00000000000080cf R12: ffff88017fbd4000
R13: ffffffffa03e3c44 R14: ffff88007492c000 R15: ffff88007492c000
FS:  00007ff8936a6940(0000) GS:ffff88017ef80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000030 CR3: 0000000177e08000 CR4: 00000000001006e0
Stack:
 ffff880176594000 ffff880173ac7948 ffffffffa0389b42 ffff880176594000
 ffff880173ac7978 ffffffffa0396e02 ffff8801765b0000 ffff88007af660d8
 0000000000000000 0000000000000004 ffff880173ac79c0 ffffffffa03b6b64
Call Trace:
 [<ffffffffa0389b42>] chv_compute_dpll.isra.39+0x33/0x55 [i915]
 [<ffffffffa0396e02>] vlv_force_pll_on+0x80/0xc6 [i915]
 [<ffffffffa03b6b64>] vlv_power_sequencer_pipe+0x29b/0x3dd [i915]
 [<ffffffffa03b6cd4>] _pp_stat_reg+0x2e/0x38 [i915]
 [<ffffffffa03b6dc1>] wait_panel_status+0x4c/0x1ec [i915]
 [<ffffffffa03b6fcb>] wait_panel_power_cycle+0x6a/0xb4 [i915]
 [<ffffffffa03b70da>] edp_panel_vdd_on+0xc5/0x1d1 [i915]
 [<ffffffffa03b861b>] intel_dp_aux_ch+0x55/0x572 [i915]
 [<ffffffff810af5c8>] ? mark_held_locks+0x5d/0x74
 [<ffffffff81518e61>] ? mutex_lock_nested+0x321/0x346
 [<ffffffff81094007>] ? preempt_count_sub+0xf2/0x102
 [<ffffffffa03b8cb4>] intel_dp_aux_transfer+0x17c/0x1b5 [i915]
 [<ffffffffa03028ef>] drm_dp_dpcd_access+0x62/0xed [drm_kms_helper]
 [<ffffffffa0302995>] drm_dp_dpcd_read+0x1b/0x1f [drm_kms_helper]
 [<ffffffffa03b5147>] intel_dp_dpcd_read_wake+0x31/0x69 [i915]
 [<ffffffffa03bb36a>] intel_dp_long_pulse+0x15f/0x5ed [i915]
 [<ffffffffa03bbb09>] intel_dp_detect+0x79/0x95 [i915]
 [<ffffffffa030340e>] drm_helper_probe_single_connector_modes+0xc7/0x3db [drm_kms_helper]
 [<ffffffffa029de23>] drm_mode_getconnector+0xe9/0x333 [drm]
 [<ffffffff810b1cfb>] ? lock_acquire+0x137/0x1df
 [<ffffffffa0292364>] drm_ioctl+0x266/0x3ae [drm]
 [<ffffffffa029dd3a>] ? drm_mode_getcrtc+0x126/0x126 [drm]
 [<ffffffff811af082>] vfs_ioctl+0x18/0x34
 [<ffffffff811af682>] do_vfs_ioctl+0x547/0x5fe
 [<ffffffff811b9acb>] ? __fget_light+0x62/0x71
 [<ffffffff811af77c>] SyS_ioctl+0x43/0x61
 [<ffffffff81001a82>] do_syscall_64+0x63/0xf8
 [<ffffffff8151bc9a>] entry_SYSCALL64_slow_path+0x25/0x25
Code: 35 00 40 a0 e8 97 4b ce e0 b8 17 00 00 00 5d c3 b8 17 00 00 00 c3 0f 1f 44 00 00 55 31 c0 31 d2 48 89 e5 53 48 8b 8f e8 01 00 00 <44> 8b 49 30 41 39 c1 7e 2d 4c 8b 51 38 4c 8b 41 40 49 83 3c c2
RIP  [<ffffffffa0389a5b>] intel_pipe_will_have_type+0x15/0x7b [i915]
 RSP <ffff880173ac7928>
CR2: 0000000000000030

The regressing patch wasn't exactly new (as in first posted more than
six months ago), so I'm a bit baffled how I didn't manage to hit this
myself so far.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Marius Vlad <marius.c.vlad@intel.com>
Reported-by: Marius Vlad <marius.c.vlad@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94995
Fixes: cd2d34d9b61f ("drm/i915: Setup DPLL/DPLLMD for DSI too on VLV/CHV")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461000844-20543-1-git-send-email-ville.syrjala@linux.intel.com
Tested-by: Marius Vlad <marius.c.vlad@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -7200,7 +7200,7 @@ static void vlv_compute_dpll(struct intel_crtc *crtc,
 		pipe_config->dpll_hw_state.dpll |= DPLL_INTEGRATED_CRI_CLK_VLV;
 
 	/* DPLL not used with DSI, but still need the rest set up */
-	if (!intel_pipe_will_have_type(pipe_config, INTEL_OUTPUT_DSI))
+	if (!pipe_config->has_dsi_encoder)
 		pipe_config->dpll_hw_state.dpll |= DPLL_VCO_ENABLE |
 			DPLL_EXT_BUFFER_ENABLE_VLV;
 
@@ -7217,7 +7217,7 @@ static void chv_compute_dpll(struct intel_crtc *crtc,
 		pipe_config->dpll_hw_state.dpll |= DPLL_INTEGRATED_CRI_CLK_VLV;
 
 	/* DPLL not used with DSI, but still need the rest set up */
-	if (!intel_pipe_will_have_type(pipe_config, INTEL_OUTPUT_DSI))
+	if (!pipe_config->has_dsi_encoder)
 		pipe_config->dpll_hw_state.dpll |= DPLL_VCO_ENABLE;
 
 	pipe_config->dpll_hw_state.dpll_md =